model: Handle (un)resolving topics.

Fixes zulip#1075
Add new get_latest_message_in_topic function to get most recent message
sent by user in the topic for which TopicInfoView is toggled.
Then check realm_community_topic_editing_limit_seconds before using
update_stream_message to edit the topic with propagate mode as
change_all to (un)resolve topics.

Author: srdeotarse

zulipterminal/model.py

@@ -30,6 +30,7 @@
 
 from zulipterminal import unicode_emojis
 from zulipterminal.api_types import (
+    RESOLVED_TOPIC_PREFIX,
     Composition,
     EditPropagateMode,
     Event,
@@ -564,6 +565,53 @@ def update_private_message(self, msg_id: int, content: str) -> bool:
         display_error_if_present(response, self.controller)
         return response["result"] == "success"
 
+    def get_latest_message_in_topic(
+        self, stream_id: int, topic_name: str
+    ) -> Dict[str, Any]:
+        request: Dict[str, Any] = {
+            "anchor": "newest",
+            "num_before": 1,
+            "num_after": 0,
+            "narrow": [
+                {
+                    "operator": "stream",
+                    "operand": self.stream_dict[stream_id]["name"],
+                },
+                {"operator": "topic", "operand": topic_name},
+            ],
+        }
+        response = self.client.get_messages(request)
+        display_error_if_present(response, self.controller)
+        return response
+
+    def toggle_topic_resolved_status(self, stream_id: int, topic_name: str) -> bool:
+        response = self.get_latest_message_in_topic(stream_id, topic_name)
+        if response["messages"] != []:
+            time_since_msg_sent = time.time() - response["messages"][0]["timestamp"]
+            edit_time_limit = self.initial_data[
+                "realm_community_topic_editing_limit_seconds"
+            ]
+            # Don't allow editing topic if time-limit exceeded.
+            if time_since_msg_sent <= edit_time_limit:
+                topic_msg_id = response["messages"][0]["id"]
+                if topic_name.startswith(RESOLVED_TOPIC_PREFIX):
+                    self.update_stream_message(
+                        topic=topic_name[2:],
+                        message_id=topic_msg_id,
+                        propagate_mode="change_all",
+                    )
+                else:
+                    self.update_stream_message(
+                        topic=RESOLVED_TOPIC_PREFIX + topic_name,
+                        message_id=topic_msg_id,
+                        propagate_mode="change_all",
+                    )
+            else:
+                self.controller.report_error(
+                    " Time limit for editing topic has been exceeded."
+                )
+        return response["result"] == "success"
+
     def update_stream_message(
         self,
         topic: str,